3rd Battalion may refer to:
- 3rd Battalion, 6th Field Artillery, a field artillery battalion of the United States Army
- 3rd Battalion, 16th Field Artillery, a field artillery battalion of the United States Army
- 3rd Battalion, 29th Field Artillery, a unit of the 3rd Brigade Combat Team
- 3rd Battalion, 69th Armor Regiment, a United States Army combined arms battalion
- 3rd Battalion, 126th Aviation Regiment, an aviation battalion of the United States Army Massachusetts National Guard
- 3rd Battalion, 153rd Infantry Regiment, a United States infantry battalion
- 3rd Battalion, 158th Aviation Regiment, an aviation battalion of the United States Army
- 3rd Battalion, 187th Infantry Regiment, an infantry battalion of the United States Army
- 3rd Battalion, 319th Field Artillery Regiment, a field artillery battalion of the United States Army
- 3rd Battalion, CEF, a battalion of the Canadian Expeditionary Force
- 3rd Battalion, Royal Anglian Regiment, the Territorial Army unit of the Royal Anglian Regiment
- 3rd Battalion, Royal Australian Regiment, a parachute infantry battalion
- 3rd Battalion, Parachute Regiment, a battalion-sized formation of the British Army's Parachute Regiment
- 3rd Battalion, The Royal Canadian Regiment, a regular force infantry battalion
- 3rd Battalion, Ulster Defence Regiment, a battalion of the British Army
- 3rd Battalion (Australia), an infantry battalion of the Australian Army
- 3rd Battalion 1st Marines, an infantry battalion in the United States Marine Corps
- 3rd Battalion 2nd Marines, an infantry battalion in the United States Marine Corps
- 3rd Battalion 3rd Marines, an infantry battalion in the United States Marine Corps
- 3rd Battalion 4th Marines, an infantry battalion of the United States Marine Corps
- 3rd Battalion 5th Marines, an infantry battalion in the United States Marine Corps
- 3rd Battalion 6th Marines, an infantry battalion in the United States Marine Corps
- 3rd Battalion 7th Marines, an infantry battalion of the United States Marine Corps
- 3rd Battalion 8th Marines, an infantry battalion in the United States Marine Corps
- 3rd Battalion 9th Marines, an infantry battalion of the United States Marine Corps
- 3rd Battalion 10th Marines, an artillery battalion of the United States Marine Corps
- 3rd Battalion 11th Marines, an artillery battalion of the United States Marine Corps
- 3rd Battalion 12th Marines, an artillery battalion of the United States Marine Corps
- 3rd Battalion 14th Marines, a reserve artillery battalion in the United States Marine Corps
- 3rd Battalion 23rd Marines, a reserve infantry battalion in the United States Marine Corps
- 3rd Battalion 24th Marines, a reserve infantry battalion in the United States Marine Corps
- 3rd Battalion 25th Marines, a reserve infantry battalion in the United States Marine Corps
- 3rd Battalion 28th Marines, an inactive infantry battalion of the United States Marine Corps